Reprinted from i Saluti, June 1996,
from the Alfa Digest
Removing A Broken Bolt or Stud
by Steve Milstein
I have a problem on my GTV6. The AC mounting bolt sheared off and left the remainder of the bolt in the aluminum engine block. I center-punched the bolt and started drilling, or rather attempting to drill. The bolt is so hard, I can’t put a hole through it!!! What can I do?
Drill into the bolt with a regular 3/8" chuck electric hand drill and use titanium nitride coated drill bits. They're gold-colored and extremely hard. The high-speed steel bits that most people have are fine for drilling sheetmetal, but not #5 bolts or harder. You MUST have a titanium bit, the more expensive the better.
- Make a starting point with a prick punch and drill a pilot hole with a 1/8" bit, then enlarge the hole with a larger bit. The final hole size in the bolt should be determined by the diameter of the bolt removal tool. This is often called an “Easy-Out.” In drilling the hole, easy does it, and it does not have to be perfectly straight, but you do want to avoid hitting the threads in the engine block. Don’t push on the bit. Let the bit chew its way through the metal, and pull it out frequently to blow out shavings. Use a variable speed drill and run the larger bit at a fairly slow speed. (The larger the drill bit or the harder the material you are drilling, the slower the drill speed should be.) You can use cutting oil, but I don’t think it’s necessary. Drill as deeply as you can with the bit, you want to get as much of the easy-out into the bolt as possible.
- Basically, an easy-out is a tapering auger with a counterclockwise twist. You thread this into the hole in the bolt, if you have the auger-type, or tap it in with a hammer if you have the type that is a tapered square prism with sharp edges on the counterclockwise edges (think of the Washington Monument, about 2" long and pushed into a hole in a bolt to be twisted counterclockwise).
- After getting the easy-out into the bolt, snugly, remove the broken bolt by twisting on the easy-out. They usually have square heads and can be turned with a taphandle or a square socket on a 1/2" drive breaker bar. You shouldn’t have to exert more torque than you normally would removing a bolt. You can use WD-40 or some other kerosene-type lubricant too.
- One trick: if you’re using WD-40, turn it out 1/2 rotation then back in 1/4 rotation. Relubricate, then repeat. This gets the lubricant spread around all the threads, rather than trying to just twist it out in one long dry twist. If there is a lot of corrosion, try this and take your time, it takes a while for the lubricant to penetrate.
- If this doesn’t work, take it to a machinist. They will get it out, but you won’t want to watch.
- Re-tap the holes before putting your next bolt in and be careful about the hardness of the replacement bolt. You can damage engine blocks by using the wrong type. If you still have the old bolt-head, there should be a marking on it, a square and some numbers.
- To avoid problems in the future, whenever you install a bolt or spark plug, use anti-seize lubricant. Don’t blame yourself for what the last guy didn’t do, though. You may hear suggestions to use heat to remove stuck fasteners. I think that is OK if you are dealing with real corroded fasteners, like plugs in the exhaust manifold or suspension bolts, but I wouldn’t do it to an aluminum engine block.